This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application PRESSURE ROLLER FOR FIXING DEVICE AND A MANUFACTURING METHOD OF THE SAME filed with the Korean Industrial Property Office on Feb. 20, 2001 and there duly assigned Serial No. 8505/2001.
1. Technical Field
The present invention relates to a pressure roller for a fixing device in a printer and a method for manufacturing the pressure roller. More particularly, the present invention relates to a pressure roller used for a fixing device and configured to achieve an improved elastic strain, and a method for manufacturing the pressure roller.
2. Related Art
Generally, a printer includes a photosensitive medium, a light scanning device, a developing device, and a fixing device. A latent image is formed on the photosensitive medium by the light scanning device, and is then developed into a toner image by the developing device. The toner image is then transferred to a sheet. The fixing device serves to firmly fix the toner image to the sheet. Typically, such a fixing device includes a transfer roller arranged to rotate while contacting the photosensitive medium, and a pressure roller arranged to rotate while contacting the transfer roller. The transfer roller is internally or externally provided with a heater which serves to maintain the transfer roller at a high temperature in order to obtain an improved transfer of the toner image from the photosensitive medium to the sheet. The pressure roller, which rotates while contacting the transfer roller at a desired pressure, is made of a material exhibiting a thermal stability and a resistance against compression.
Exemplars of recent efforts include the FIXING APPARATUS OF Ota et al., U.S. Pat. No. 6,266,509; THE IMAGE HEATING APPARATUS of Kitamura et al., U.S. Pat. No. 6,173,131 and; FIXING APPARATUS of Haneda et al., U.S. Pat. No. 6,157,805.
The pressure roller typically includes a shaft and a resin tube. A silicone rubber layer is interposed between the resin tube and the shaft.
In order to manufacture a pressure roller having the above mentioned configuration, the resin tube is fitted in a mold having the shape of a pipe with a circular cross section. The shaft is then concentrically arranged in the resin tube in a fixed state. That is, the shaft is supported by the mold so that it is maintained in a fixed state. The shaft has an outer diameter which is less than the inner diameter of the resin tube by a desired amount.
Under a condition in which the shaft is maintained in a fixed state in the resin tube, liquid-phase silicone rubber is injected between the inner surface of the resin tube and the outer surface of the shaft. As moisture contained in the liquid-phase silicone rubber is vaporized, a porous silicone rubber layer is formed. In order to allow the silicone rubber layer to come into tight contact with the resin tube, the entire inner surface of the resin tube is subjected to an etching treatment. An adhesive is also coated on the etched inner surface of the resin tube.
After completion of the formation of the silicone rubber layer, the molded product is removed from the mold. Thus, manufacture of the pressure roller is completed.
The silicone rubber layer interposed between the inner surface of the resin tube and the outer surface of the shaft should have a porous structure which is formed by vaporization. To this end, a low temperature vulcanizing (LTV) silicone rubber is used as the material of the silicone rubber layer in order to achieve formation of pores in a temperature range not causing deformation of the resin tube. However, such LTV silicone rubber is expensive as compared to high temperature vulcanizing (HTV) silicone rubber which is foamed at a high temperature of about 120xc2x0 C. to form pores.
Furthermore, the pressure roller described above has a high manufacturing cost because the entire inner surface of the resin tube must be subjected to an etching treatment in order to allow the silicone rubber layer to come into tight contact with the resin tube.
In addition, the pressure roller should exhibit an elastic strain sufficient to reduce the pressure of the pressure roller against the transfer roller while allowing the pressure roller to have a contact surface with superior flatness. However, the silicone rubber layer described above exhibits a high degree of hardness. As a result, there is a disadvantage in that it is necessary to increase the pressure to be applied to the transfer roller.
The present invention has been developed in view of the above mentioned problems, and an object of invention is to provide an improved pressure roller and method of manufacturing such a pressure roller for a fixing device.
It is also an object to provide a pressure roller for a fixing device and a method of manufacturing such a pressure roller which uses HTV silicone rubber exhibiting a foamability at a high temperature, thereby reducing manufacturing cost while exhibiting a desired elastic strain at a low pressure.
In accordance with one aspect, the present invention provides a pressure roller for a fixing device, that may be constructed with a shaft; a first silicone rubber layer formed on the shaft as an axially elongate cylindrical layer so as to surround the shaft and the first silicone rubber layer; a resin tube formed on the first silicone rubber layer so as to surround the shaft, the resin tube having extensions at opposite ends thereof, each extension extending beyond an opposite end of the first silicone rubber layer; and second silicone rubber layers, each formed at a respective axially opposite end of the first silicone rubber layer between the extensions of the resin tube and the shaft, the second silicone rubber layers serving to couple the first silicone rubber layer to the resin tube.
In accordance with another aspect, the present invention provides a pressure roller for a fixing device, that may be constructed with a shaft; a silicone rubber layer extruded on the shaft as an axially elongate cylindrical layer using an extruder so as to surround the shaft, and foamed so as; to have a number of pores; and a resin tube bonded by adhesive to the silicone rubber layer while surrounding the silicone rubber layer.
In accordance with another aspect, the present invention provides a method for manufacturing a pressure roller for a fixing device by forming a silicone rubber layer by extruding silicone rubber on a shaft with an extruder, and curing the extruded silicone rubber to foam the silicone rubber, thereby forming a silicone rubber layer having a number of pores. A resin tube forms a cylindrical sheath that surrounds and encases the silicone rubber layer. The resin tube is bonded to the silicone rubber layer with an adhesive while surrounding the silicone rubber layer.